Explain why the cutoff condition for a carrier-concentration-reduction type waveguide is independent of wavelength. We desire an epitaxially-grown double-heterojunction In(1-x)GaxAs(1-y)Py waveguide...

Explain why the cutoff condition for a carrier-concentration-reduction type

waveguide is independent of wavelength.

We desire an epitaxially-grown double-heterojunction In(1-x)GaxAs(1-y)Py

waveguide that will have a bandgap Eg = 1.1ev in the waveguiding layer at

room temperature.

(a) If lattice-matched layers are desired, what should be the relative concentrations of the constituent elements? i.e. What are x and y?

(b) What is the shortest wavelength that can be guided in this waveguide

without excessive interband absorption?